甘かった。(but this seems like a very strange word to use for sushi... Maybe you wanted to say おいしかった. 甘い=sweet, おいしい=tasty/delicious)

It's awkward, it seems that 甘い can both be read as うまい - delicious; appetizing; appetising, and あまい - sweet. My dictionary said that the latter is usually written using kana alone, so I thought I could safely use 甘い to mean うまい to get some variety in the vocabulary.